Drip irrigation systems usually include a continuous irrigation water supply line with emitter-type drippers installed along the line, usually at regular intervals. (The terms "emitter" and "dripper" are used interchangeably to refer to the pressure-reducing element of the system.) Irrigation water flows through the supply line under pressure, and a small amount of water continuously drips out at the intervals where the drippers are located. Drip irrigation has proved to be highly successful in producing greater growth of vegetation with the same amount of water, when compared with conventional irrigation techniques.
A number of different drip irrigation systems have been used in the past. They vary from the cheapest and simplest systems, namely, a hole in the wall of a water supply line, to expensive and complex multi-component dripper units.
Perhaps the most practical of the prior drip irrigation systems involves use of separate drip emitters or drippers installed in or on the supply line. The dripper taps off a portion of the water flowing in the water supply line and passes the water through a labyrinth or other meandering or circuitous path that produces a large pressure drop in the water and discharges it at a uniform drip rate. Generally, such pressure-reducing labyrinthine drippers are successful because they use a large enough hole in the supply pipe and a wide enough passage through the labyrinth to avoid clogging in most cases, while they also operate at reasonably high line pressures.
The present invention is directed to the problem of developing an economic drip irrigation system for low value crops where it is essential to reduce the capital costs for a precise system to a level lower than that achieved by drip irrigation systems presently available.
There are low cost drip irrigation systems presently available that are made from thin plastic film, as thin as 0.004 inch in wall thickness. These products are not easy to use because of the low strength of the film, and they commonly are used for one growing season only and then thrown away. There are similar drip irrigation systems with wall thicknesses up to about 0.02 inch, and if buried, they will last for many crops, but these systems have problems with root intrusion. In addition, the management to operate these systems for several crops is very difficult, and thus excludes most growers.
U.S. Pat. No. 5,310,438 to Ruskin discloses a method for making low cost drip irrigation systems having an extended life beyond the growing season of one crop. The drip irrigation lines can be used effectively for multiple growing seasons or multiple crops in sequence over an extended period of time. The drip irrigation system disclosed in the '438 patent also carries herbicides such as trifluralin to keep invasive roots out of the dripper system.
The present invention is based on a recognition of disadvantages with the process disclosed in the '438 patent. According to the present invention, drip irrigation lines are comparatively easier to manufacture, particularly as a result of a method used for feeding a sequence of drippers to an extruded plastic film to which the drippers are bonded. As a result, production speed is greatly increased, particularly with the simultaneous production of multiple drip irrigation lines. In addition, the film wall strength adjacent each emitter is improved compared to the '438 process. The process of this invention also eliminates the additional steps of punching inlet holes into the drippers, which was characteristic of the '438 process. Further, the finished drip irrigation lines produced by the present method can easily incorporate multiple small holes into each dripper to act as a filter, which was absent from the '438 process.